At present, touch screens are a newest type of information input devices, which support human-computer interaction in a simple, convenient and natural manner, and are the most modern interactive multimedia devices. A capacitive touch screen has such advantages as rapid touch response, multi-touch capability, etc. A single-layer on-cell capacitive touch screen has such advantages as a low weight and a small thickness, low manufacturing cost, integration of touch and display, etc. The single-layer on-cell capacitive touch screen that supports frame adhesion is widely preferred by end users for its advantages such as inexpensive materials for the outer layer for bonding, simplicity of process, convenience of repair, etc.
In a frame adhesion structure, there is a layer of air between the outer layer and touch sensors. Since the dielectric constant of air is lower than those of other materials (e.g., liquid optical clear adhesive (LOCA)), electric field sensing (i.e., capacitive coupling) between touch driving electrodes and touch sensing electrodes is weakened with the result that touch signals are significantly reduced and the touch performance is degraded. One solution for enhancement of touch signals is to simply increase the two-dimensional size (length and width) of individual driving electrodes and sensing electrodes; however, the center-to-center spacing between adjacent electrodes is increased accordingly. In consequence, the minimum of discrimination spacing for two fingers is significantly increased and the linearity is significantly deteriorated, seriously affecting the overall touch performance.
Therefore, it has become very important to ensure good touch performance without changing other materials of the whole on-cell touch screen module.